    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.configuration2.tree;
    018
    019/**
    020 * <p>
    021 * Definition of a <em>Visitor</em> interface for a configuration node
    022 * structure.
    023 * </p>
    024 * <p>
    025 * This is a typical application of the GoF <em>Visitor</em> pattern. An object
    026 * implementing this interface can be used to traverse a hierarchical structure
    027 * of nodes in various ways. The type of the nodes in the structure is generic;
    028 * a corresponding {@link NodeHandler} implementation must be available for
    029 * navigating through the structure.
    030 * </p>
    031 * <p>
    032 * Note that the exact way the methods of a {@code ConfigurationNodeVisitor} are
    033 * invoked is dependent on a specific traversal process.
    034 * </p>
    035 *
    036 * @since 1.3
    037 * @version $Id: ConfigurationNodeVisitor.java 1624601 2014-09-12 18:04:36Z oheger $
    038 * @param <T> the type of the nodes processed by this visitor
    039 */
    040public interface ConfigurationNodeVisitor<T>
    041{
    042    /**
    043     * Visits the specified node before the children of this node - if existing
    044     * - are processed.
    045     *
    046     * @param node the node to be visited
    047     * @param handler the {@code NodeHandler}
    048     */
    049    void visitBeforeChildren(T node, NodeHandler<T> handler);
    050
    051    /**
    052     * Visits the specified node after after its children - if existing - have
    053     * been processed.
    054     *
    055     * @param node the node to be visited
    056     * @param handler the {@code NodeHandler}
    057     */
    058    void visitAfterChildren(T node, NodeHandler<T> handler);
    059
    060    /**
    061     * Returns a flag whether the current visit process should be aborted. This
    062     * method allows a visitor implementation to state that it does not need any
    063     * further data. It may be used e.g. by visitors that search for a certain
    064     * node in the hierarchy. After that node was found, there is no need to
    065     * process the remaining nodes, too. This method is called after each
    066     * visited node. A result of <strong>true</strong> indicates that the
    067     * current iteration is to be aborted.
    068     *
    069     * @return a flag if the visit process should be stopped
    070     */
    071    boolean terminate();
    072}